Tubes are employed on vehicles to transport exhaust gases generated by the vehicular engine to a location on the vehicle from which the exhaust gases can be emitted safely. The exhaust system is generally relegated to a space that has not previously been committed to other structural and operational components of the vehicle. Additionally, the exhaust system must provide a specified clearance from certain other components of the vehicle, and must be disposed in visually unobtrusive places on passenger cars and many small trucks. In view of these various limitations, the tubular components of exhaust systems invariably must be bent to follow a very circuitous path. Additionally, the circuitous path required for tubular exhaust products will vary substantially from one vehicle model to the next.
The cross sectional area of an exhaust pipe is determined in part by the volume of exhaust gases produced by the engine. Large trucks will generally require exhaust pipes with cross sectional dimensions much greater than the corresponding pipes on passenger cars. Larger diameter pipes are of course much more expensive than smaller diameter pipes and therefore bending errors in large pipes can be very costly. The exhaust pipes of many trucks extend to an elevated position on the vehicle, and therefore are visually apparent. In many instances these exhaust pipes are formed from stainless steel to provide some degree of aesthetic attractiveness. Stainless steel exhaust system components can be significantly more expensive than exhaust components made from other materials. As the number of components and accessories on vehicles increases, the limited space available for exhaust system components diminishes. As a result, the tubular exhaust system components often must be manufactured with great precision to ensure that the exhaust system is retained in the minimal space that has been allotted to it. Even a small angular error in a bend at one end of an exhaust pipe can result in a significant displacement error at the opposed end of the pipe.
Tubular stock material has been used to manufacture other components of vehicles. For example, rectangular tubes recently have been employed to manufacture vehicular frames. Rectangular tubes used for vehicular frames generally do not require the extreme bends required for exhaust pipes. However, the rectangular frame rails must be bent with extreme precision to ensure proper mating with other structural components of the vehicle.
Pipe or tube benders typically comprise at least a bend die, a clamp die and a pressure die. The bend die includes an arcuate surface which defines the inner circumference of each bend formed by the bending apparatus. The clamp die is disposed radially outwardly from the bend die, and is operative to clamp the tube to be bent between the clamp die and the bend die. The pressure die also is disposed at a radially outer position of the tube to be bent, and is initially adjacent to and aligned with the clamp die. The clamp die and the bend die are operative to rotate in unison relative to the pressure die, and to thereby bend the tube. Although the radius of curvature is determined by the physical dimensions of the bend die, the degree of curvature can readily be determined by the amount of rotation of the bend die and clamp die. Most benders also include a wiper die which is disposed in generally opposed relationship to the pressure die and adjacent to the bend die. The wiper die and the pressure die thus define the tangent at the trailing end of each bend. In most vehicular tube bending operations, a mandrel will also be disposed within the tube to ensure that the tube does not deform excessively in response to the bending forces. Additionally, many benders will include a pressure die booster which exerts an axial force on the pressure die to urge the pressure die toward the clamp die during a bending operation. The pressure die booster is intended to push the tube into the bend, thereby reducing the amount of thinning that might otherwise occur on the outer circumferential wall of each bend. After the tube has been bent by the prior art apparatus, at least one end of the bent tube may be presented to a sizer which wedges or otherwise alters the cross section of the tube to mate with another exhaust system component.
Programmable benders have been available for many years. The typical programmable bender includes all of the above described components, and further includes a programmably movable collet which is operative to grip the trailing end of each tube to be bent. The collet is operative to undergo selective rotations and axial movements to properly position the tube for each sequential bend. The rotational movements of the bend die and the clamp die are also programmed. Thus, the collet will axially and rotationally position the tube relative to the bend die, and the bend die and clamp die will cooperate to effect a preprogrammed bend. Upon completion of the bend, the collet will axially and rotationally position the pipe for the next sequential bend.
Even with the above described programmable benders, bending errors are known to exist. For example, in some situations the metallurgical characteristics of a particular tube will cause the tube to spring back after the bending forces have been released. This spring-back will vary from one tube to the next and cannot readily be predicted. In other situations, the momentum caused by movements in the leading end of the tube will generate bending moments in addition to the bending forces generated by the apparatus. A very efficient bending apparatus to control these problems is shown in U.S. Pat. No. 4,732,025 which issued to Gerald R. Trudell and Terrance C. Marlinga on Mar. 22, 1988 and which is assigned to the assignee of the subject application. The apparatus disclosed in U.S. Pat. No. 4,732,025 includes a position sensing device which is operative to sense the location of a leading portion of the tube to determine if the leading portion of the tube is in prespecified positions at various stages of the bending process. The disclosure of U.S. Pat. No. 4,732,025 is incorporated herein by reference.
An apparatus for bending rectangular tubes, such as the rectangular tubes used in the above described vehicular frames is disclosed in U.S. Pat. No. 4,744,233 which issued to Gerald R. Trudell on May 17, 1988 and which also is assigned to the assignee of the subject invention. The apparatus disclosed in U.S. Pat. No. 4,744,233 includes movable components in the pressure die, movable components in the clamp and an improved mandrel, each of which improves efficiency in bending rectangular tubes. The disclosure of U.S. Pat. No. 4,744,233 also is incorporated herein by reference.
Despite the advantages achieved with the above referenced U.S. Pat. No. 4,732,025 and U.S. Pat. No. 4,744,233, it is desired to provide even further improvements in programmable tube benders. For example, it has been found that differences in metallurgical characteristics will cause tubes to respond differently to the forces generated during bending. In particular, it is known that some tubes will fail in response to the forces generated by the bender while others will not. Failures typically will be defined by either a rupture in an outer wall of a bend or a collapsing adjacent an inner wall of a bend. These problems are particularly likely to occur in large diameter tubes where the wall thickness represents a relatively smaller proportion of the total diameter. These problems are also more likely in tubes subjected to one or more bends defining relatively large degrees of curvature. As noted above, large diameter tubes are expensive, particularly those manufactured from stainless steel. A high percentage of failures in such tubes can be extremely costly even if the raw material in the pipe can be salvaged for scrap value. Similarly, even small diameter tubes that fail when subjected to high degrees of curvature represent costly losses. A substantial part of these cost penalties are attributable to the labor and machine time that has been devoted to making the stock material into a tube and at least beginning the bending operations on the tube.
In view of the above, it is an object of the subject invention to provide a tube bender that is operative to create a plurality of precise bends in a tube.
It is another object of the subject invention to provide a tube bender that is operative to substantially minimize failures attributable to bending.
It is an additional object of the subject invention to provide a tube bending apparatus that is operative to sense changes in bending conditions, and alter the operation of the bender to accommodate the sensed changes in bending conditions.
Still a further object of the subject invention is to provide a tubebending apparatus that enables bends of relatively high degrees of curvature to be placed in relatively close proximity to one another with a significantly reduced likelihood of failure.